Wheel-hub gears and casings therefor

ABSTRACT

A gear casing for a wheel-hub assembly comprises a gear housing comprising a drive-gear volume for accommodating therewithin a gearing assembly that is positioned to mediate between a drivetrain member and a wheel-hub member, the drive-gear volume being in fluid communication with opposing first and second openings formed in the gear housing for respective gearing-assembly connections therethrough with the drivetrain member and the wheel hub member; and a lubricant compartment radially displaced from the drive-gear volume and in fluid communication therewith exclusively via an array of one or more lubricant passages disposed circumferentially around a portion of the gear housing, the lubricant-passage array arranged for flow therethrough of a gearing-assembly lubricant between the lubricant compartment and the gear housing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of PCT applicationPCT/IB2021/060232, filed on Nov. 4, 2021, which is incorporated hereinby reference in its entirety. PCT application PCT/IB2021/060232 claimsthe benefit of U.S. Provisional Patent Application No. 63/111,155, filedon Nov. 9, 2020, which is also incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The present invention relates to gearing assemblies for transmittingtorque to drive wheels of vehicles and to casings therefor, andparticularly to assemblies and casings for individually-geared drivewheels.

BACKGROUND

Vehicle drivetrains and gearing arrangements have been developed andimproved over the course of more than a century, resulting insophisticated designs that serve to distribute forces to the variouswheels of a vehicle.

There is a need for a compact powertrain gear mounted to the wheel hubto motorize the wheel. A compact gear may be defined as such havingminimum lateral size to allow other wheel assembly components within thevolume of the wheel and between the wheel and the vehicle chassis. Thereare examples of gears coupled to a wheel hub, which are either too long,integrated with a motor within the volume of the wheel, and/or have alow reduction ratio between the motor and the wheel hub. Some such geararrangements are lubricated by using a wet sump, wherein a space belowthe gear is required for oil reservoir and an oil pump is used for oilcirculation. Some gear arrangements are lubricated by using a dry sumpand oil pump (e.g. scavenge pump) to supply oil to the gear. There istherefore a need for a compact wheel-hub gear that is self-lubricated,i.e., without a pump, by an amount of oil in a range that providessufficient lubrication without overflowing the gear.

SUMMARY

According to embodiments of the invention, a gear casing for a wheel-hubassembly comprises: (a) a gear housing comprising a drive-gear volumefor accommodating therewithin a gearing assembly that is positioned tomediate between a drivetrain member and a wheel-hub member, thedrive-gear volume being in fluid communication with opposing first andsecond openings formed in the gear housing for respectivegearing-assembly connections therethrough with the drivetrain member andthe wheel hub member; and (b) a lubricant compartment radially displacedfrom the drive-gear volume and in fluid communication therewithexclusively via an array of one or more lubricant passages disposedcircumferentially around a portion of the gear housing, thelubricant-passage array arranged for flow therethrough of agearing-assembly lubricant between the lubricant compartment and thegear housing.

In some embodiments, the gear casing can comprise a plurality of casingportions, wherein at least one of the gear housing and the lubricantcompartment is formed by a joining of at least two of the plurality ofcasing portions. each of the joined casing portions comprising at leasta part of a respective interior surface of at least one of the gearhousing and the lubricant compartment. In some such embodiments, boththe gear housing and the lubricant compartment can be formed by thejoining. In some embodiments, the lubricant-passage array can be formedexclusively in one joined casing portion. In some embodiments, theplurality of casing portions can include a gasket interposed between twoother casing portions of the plurality of casing portions, and/or thelubricant-passage array can be formed in the gasket.

In some embodiments, the lubricant-passage array can comprise aplurality of discrete lubricant passages. In some such embodiments, abottommost one of the lubricant passages can be disposed to be at leastin part below a central axis of the gearing assembly, and/or a topmostone of the lubricant passages can be disposed to be at least in partabove the central axis of the gearing assembly. In some embodiments, atleast a part of the bottommost lubricant passage can be lower than alowest part of the drive-gear volume. In some embodiments, the gearcasing can be arranged such that a majority of a lubricant-flow througha bottommost lubricant passage is from the lubricant compartment to thegear housing, and/or a majority of a lubricant-flow through a topmostlubricant passage is from the gear housing to the lubricant compartment.

In some embodiments, the gear casing can be configured such that alllubricant flows between the lubricant compartment and the gear housingare due to forces generated by operation of the gearing assembly and/orexternal forces acting upon the wheel-hub assembly.

In some embodiments, the gear casing can additionally comprise, withinthe lubricant compartment, a flow-regulation element.

In some embodiments, the gear casing can additionally comprise a firstconnection portion adapted for connection to a suspension arm of a wheelassembly and a second connection portion adapted for connection to asteering-system member of the wheel assembly.

In some embodiments, the gear casing can comprise a plurality oflubricant compartments radially displaced from the drive-gear volume,each lubricant compartment being in fluid communication therewithexclusively via a respective array of one or more lubricant passagesdisposed circumferentially around a portion of the gear housing, therespective lubricant-passage arrays being arranged for flow therethroughof a gearing-assembly lubricant between the lubricant compartment andthe gear housing.

According to embodiments, a wheel assembly can comprise (a) the gearcasing of any of the embodiments disclosed hereinabove, and/or (b) thegearing assembly positioned to mediate between the drivetrain member andthe wheel-hub member, the gearing assembly disposed within in the gearcasing and comprising a compound planetary gear train comprising (i) asun gear in bearinged connection with the drivetrain member of thevehicle so as to be rotated thereby, (ii) a carrier in bearingedconnection with the wheel-hub member, and/or (iii) a plurality ofcomposite planet gears each having multiple radii. In some suchembodiments, the bearinged connection with the wheel-hub member can bevia a wheel-hub bearing assembly interiorly attached to the gear casing.In some embodiments, the planet gears can be meshed with a ring gearinteriorly attached to the gear casing.

In some embodiments, the wheel assembly can additionally comprise: (a) asub-frame configured to be mounted to a reference frame of a vehicle;(b) a suspension arm linking the sub-frame to a first connection portionof the gear casing; and/or (c) a steering system member connecteddistally to a second connection portion of the gear casing andconfigured to rotate the wheel-hub member about a steering axis.

In some embodiments, the wheel assembly can additionally comprise thedrivetrain member, the wheel-hub member coupled to the gearing assembly,and/or a brake assembly coupled to the wheel-hub member, the brakeassembly being characterized by having a brake caliper connectedthereto, wherein a thickness of the gear housing through the drive-gearvolume is less than 120% of a width of the brake caliper, the thicknessand the width both being in a direction parallel to a central axis ofthe gearing assembly. In some such embodiments, a thickness of thegearing assembly can be less than 110% of a width of the brake caliper,the thickness and the width both being in a direction parallel to acentral axis of the gearing assembly. In some embodiments, the gearingassembly can be disposed entirely between the wheel-hub member and aplane defined by an inward-facing rim of a wheel mounted to thewheel-hub member.

According to embodiments, a vehicle can comprise: a pair of opposingwheel assemblies, the wheel assemblies being according to any of theembodiments disclosed hereinabove, a corresponding pair of wheels,and/or the reference frame. In some embodiments, the lubricationcompartment of the gear casing of each wheel assembly can be displacedfrom the respective drive-gear volume so as to be forward of the gearingassembly.

According to embodiments of the invention, a gear casing comprises firstand second gear-casing portions joined to each other to form (i) a gearhousing comprising a drive-gear volume for accommodating therewithin agearing assembly that is positioned to mediate between a drivetrainmember and a wheel-hub member, and (ii) a lubricant compartment forstoring a quantity of a gearing-assembly lubricant, the lubricantcompartment radially displaced from the drive-gear volume and in fluidcommunication therewith exclusively via an array of one or morelubricant passages arranged circumferentially around a portion of thegear housing.

In some embodiments, the array of lubricant-passages can be formedexclusively in a specific one of the first and second joined gear-casingmembers.

In some embodiments, a first gear-casing portion can comprise a firstconnection portion adapted for connection to a suspension arm of a wheelassembly and a second connection portion adapted for connection to asteering-system member of the wheel assembly.

In some embodiments, a thickness of the lubrication compartment can beless than half a thickness of the gear housing through the drive-gearvolume, both of the thicknesses being in a direction parallel to acentral axis of the gearing assembly.

In some embodiments, the gear casing can additionally comprise a brakeassembly characterized by having a brake caliper connected thereto,wherein a thickness of the gear housing through the drive-gear volume isless than 120% of a width of the brake caliper, the thickness and thewidth both being in a direction parallel to a central axis of thegearing assembly.

According to embodiments, an assembly can comprise (a) the gear casingaccording to any of the embodiments disclosed hereinabove, and/or (b)the gearing assembly positioned to mediate between the drivetrain memberand the wheel-hub member, the gearing assembly disposed within the gearcasing and comprising a compound planetary gear train comprising (i) asun gear in bearinged connection with the drivetrain member of thevehicle so as to be rotated thereby, (ii) a carrier in bearingedconnection with the wheel-hub member, and/or (iii) a plurality ofcomposite planet gears each having multiple radii.

In some embodiments, a thickness of the gearing assembly can be lessthan 110% of a width of the brake caliper, the thickness and the widthboth being in a direction parallel to a central axis of the gearingassembly.

In some embodiments, the bearinged connection with the wheel-hub membercan be via a wheel-hub bearing assembly interiorly attached to the gearcasing.

In some embodiments, the planet gears cam be meshed with a ring gearinteriorly attached to the gear casing.

According to embodiments of the present invention, an assembly comprises(a) a gearing assembly for transmitting rotation to a wheel of avehicle, and (b) a gear housing for housing the gearing assemblytherein, the gearing assembly comprising a compound planetary gear trainconfigured (i) for a sun gear thereof to be in bearinged connection witha drivetrain member of the vehicle so as to be rotated thereby, and/or(ii) for a carrier thereof to be in bearinged connection with awheel-hub member of the vehicle so as to rotate the wheel-hub member,the bearinged connection with the wheel-hub member being via a wheel-hubbearing assembly interiorly attached to the gear housing, the sun gearand the carrier being rotatably linked by a plurality of compositeplanet gears each (i) having multiple radii and arranged to rotate thecarrier, and/or (ii) meshed with a ring gear interiorly attached to thegear housing.

According to embodiments of the invention, a wheel assembly comprises:(a) a gearing assembly comprising a compound planetary gear trainconfigured (i) for a sun gear thereof to be in bearinged connection witha drivetrain member of the vehicle so as to be rotated thereby, and/or(ii) for a carrier thereof to be in bearinged connection with awheel-hub member of the vehicle so as to rotate the wheel-hub member,the sun gear and the carrier being rotatably linked by a plurality ofcomposite planet gears each having multiple radii and arranged to rotatethe carrier; and (b) a gear casing comprising: (i) a gear housingcomprising a drive-gear volume accommodating therewithin the gearingassembly, the gearing assembly positioned to mediate between adrivetrain member and a wheel-hub member, the drive-gear volume being influid communication with opposing first and second openings formed inthe gear housing for respective gearing-assembly connectionstherethrough with the drivetrain member and the wheel hub member; and(ii) one or more lubricant compartments radially displaced from thedrive-gear volume, each one of the one or more lubricant compartmentsbeing in fluid communication with the drive-gear volume exclusively viaa respective array of one or more lubricant passages disposedcircumferentially around a respective portion of the gear housing, eachlubricant-passage array arranged for flow therethrough of agearing-assembly lubricant between the respective lubricant compartmentand the gear housing.

In some embodiments, the wheel assembly can additionally comprise thewheel-hub member, wherein the gearing assembly is disposed entirelybetween the wheel-hub member and a plane defined by an inward-facing rimof a wheel mounted to the wheel-hub member.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described further, by way of example, withreference to the accompanying drawings, in which the dimensions ofcomponents and features shown in the figures are chosen for convenienceand clarity of presentation and not necessarily to scale. In thedrawings:

FIG. 1 is a schematic front-view drawing of a left wheel assemblyaccording to embodiments of the present invention.

FIG. 2 is a schematic front-view of a portion of a vehicle comprisingwheel assemblies according to embodiments of the present invention.

FIGS. 3A and 3B are, respectively, inward-facing perspective and frontview schematic drawings of a gear casing comprising a gear housing and alubrication compartment according to embodiments of the presentinvention.

FIGS. 4A and 4B are, respectively, inward-facing perspective andinward-facing elevation views of a gearing assembly according toembodiments of the present invention.

FIGS. 5A and 5B are, respectively, inward-facing and outward-facingelevation views of an assembly comprising the gear casing of FIGS. 3A-Band the gearing assembly of FIGS. 4A-B.

FIG. 6A is a schematic front-view drawing of the assembly of FIGS.5A-5B, also having connected a driveshaft, a brake assembly and awheel-hub member, according to embodiments of the present invention.

FIG. 6B is a sectional inward-facing view of the assembly of FIG. 6A,according to embodiments of the present invention.

FIG. 7 is a schematic drawing of a gear casing comprising a gear housingand two lubrication compartments, according to embodiments of thepresent invention.

FIGS. 8A and 8B are exploded views of a gear casing formed by joiningtwo portions, according to embodiments of the present invention.

FIG. 9 is a schematic drawing of a gasket for sealing between two joinedportions of a gear casing, according to embodiments of the presentinvention.

FIG. 10A is an outward-facing elevation view of the assembly of FIG. 6A,also having a brake caliper mounted to the brake assembly, according toembodiments of the present invention.

FIG. 10B is a partial front view of the assembly of FIG. 10A, indicatingthe respective widths of a gear housing and a lubricant compartment,according to embodiments of the present invention.

FIG. 10C is a rear view of the assembly of FIGS. 10A-B, indicating therespective widths of the brake caliper, the gearing assembly and thegear housing, according to embodiments of the present invention.

FIG. 11 is a schematic cutaway front view of the assembly of FIGS. 5A-Balso having connected a wheel-hub member and mounted to a wheel,indicating the respective widths of the gearing assembly and the wheel,according to embodiments of the present invention.

FIG. 12 is a schematic, cutaway outward-facing view of the assembly ofFIGS. 5A-5B, indicating a prevailing lubricant flow direction and alubricant level, according to embodiments of the present invention.

FIG. 13 shows the cutaway assembly view of FIG. 12, indicating sectionsof a lubricant compartment according to embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The invention is herein described, by way of example only, withreference to the accompanying drawings. With specific reference now tothe drawings in detail, it is stressed that the particulars shown are byway of example and for purposes of illustrative discussion of thepreferred embodiments of the present invention only, and are presentedin the cause of providing what is believed to be the most useful andreadily understood description of the principles and conceptual aspectsof the invention. In this regard, no attempt is made to show structuraldetails of the invention in more detail than is necessary for afundamental understanding of the invention, the description taken withthe drawings making apparent to those skilled in the art how the severalforms of the invention may be embodied in practice. Throughout thedrawings, like-referenced characters are generally used to designatelike elements.

Note: Throughout this disclosure, subscripted reference numbers (e.g.,10₁ or 10_(A)) may be used to designate multiple separate appearances ofelements of a single species, whether in a drawing or not; for example:10₁ is a single appearance (out of a plurality of appearances) ofelement 10. The same elements can alternatively be referred to withoutsubscript (e.g., 10 and not 10₁) when not referring to a specific one ofthe multiple separate appearances, i.e., to the species in general.

For convenience, in the context of the description herein, various termsare presented here. To the extent that definitions are provided,explicitly or implicitly, here or elsewhere in this application, suchdefinitions are understood to be consistent with the usage of thedefined terms by those of skill in the pertinent art(s). Furthermore,such definitions are to be construed in the broadest possible senseconsistent with such usage.

Embodiments of the present invention include the provision of gearingassemblies for wheels of a vehicle, i.e., each geared wheel is pairedwith a gearing assembly that mediates between a driveshaft or otherdrivetrain member and the respective wheel hub of the wheel. Thedriveshaft transmits a torque from a motor (for example, an electricmotor) to rotate a first gear or group of gears of the gearing assembly,for example via a constant-velocity joint or other suitable arrangement.The gearing assembly is designed to transmit torque to the wheel hub,e.g., at a reduced speed or rotation relative to the received torque. Inpreferred designs, the motor is associated with a reference frame of thevehicle or with a modular sub-frame mounted thereto, such that the motoris ‘sprung’ with respect to the vehicle's suspension system. On theother hand, the gearing assembly, which is preferably in closeconnection with the wheel hub and wheel, is typically ‘unsprung’ weight.In addition, an independently-driven and/or independently-suspendedand/or independently-steered wheel is typically integrated in a wheelassembly with many moving parts in a relatively small space. Thus it canbe desirable for the gearing assembly, and a gear housing provided toaccommodate the gearing assembly, to be both compact and lightweight.

Unless otherwise indicated, a ‘wheel assembly’ as used herein means anassembly for supporting a wheel of a vehicle according to any of theembodiments disclosed herein and wheel-assembly components such as (andnot exhaustively): gearing assemblies, gear casings and lubricationarrangements; steering systems and suspension systems; wheel hubs, brakesystems, and driveshafts. A wheel assembly can be mounted to a‘reference frame’ of a vehicle, e.g., a chassis or similar vehicleframe, although the mounting need not necessarily be done ‘as a unit’. Awheel assembly may include a ‘sub-frame’ to which some or all of theassembly components are mounted or otherwise attached such that thesub-frame mediates between the reference frame and the various wheelassembly components. The term ‘sub-frame’ should be understood to meanany rigid frame or one or more structural elements in fixed combination.The ‘sub’ prefix is intended to distinguish the sub-frame from a mainframe or reference frame of the vehicle. A wheel assembly may or may notinclude an electric motor and/or the wheel itself.

When used in this specification and in the claims appended hereto, theword ‘vehicle’ is to be understood as referring to a motorized vehiclehaving one or more wheels. Non-limiting examples of a vehicle, accordingto this definition, are a vehicle with motive power provided by anonboard engine, and an ‘electric vehicle’ powered, when in motion, byone or more electric motors and a battery or other energy storage deviceonboard. The battery need not be provided with the vehicle, or installedin the vehicle, unless and until the vehicle is in motion. The word‘vehicle’ should also be understood as encompassing a “vehicle platform”comprising at least a chassis (or other ‘reference frame’ to which wheelassemblies can be mounted) and one or more wheels. A ‘vehicle platform’need not necessarily comprise, at the time of providing the vehicleplatform, all of the accoutrements required for transport of passengersand/or cargo such as vehicle-body components or interior furnishings.

According to embodiments disclosed herein, a compact, lightweight gearcasing for housing therein a gearing assembly can serve as a wheelinterface, or ‘upright’, supporting a wheel-hub assembly that comprisesone or more wheel-hub members. The gear casing can be designed to make aconnection with a steering rod, e.g., a ‘pushrod’, and in this way thegear casing can transmit a steering torque from the steering rod to thewheel-hub assembly so as to rotate the wheel around a steering axis.Additionally or alternatively, the gear casing can be designed toreceive one or more bearing arrangements, including, in a non-limitingexample, ball joints, so as to make a bearinged connection with one ormore respective suspension-assembly members.

As will be described in further detail hereinbelow, the size and weightof the gear casing and gearing assembly can be reduced relative to priorart designs. Inter alia, this can be accomplished by integrating acompact, lightweight gear-lubrication arrangement in the gear casing,and in particular an arrangement for pumpless oil lubrication. The term‘pumpless’ means without a specific or dedicated pump component; in apumpless configuration, internal flow and circulation of oil aresubstantially due to forces generated by operation of the gearingassembly itself and/or external forces acting upon the wheel-hubassembly. Inter alia, this can be accomplished by minimizing the sizeand weight of the gearing assembly by employing a compound planetarygear train design.

Referring now to the figures and in particular to FIG. 1, a wheelassembly 150 for a vehicle comprises a gear casing 350 according to anyof the embodiments disclosed herein. In embodiments, the gear casing 350has a gearing assembly (not seen in FIG. 1) installed therein fortransmitting torque from a driveshaft member 180 to a wheel-hub member174. In some embodiments, the gear casing 350 serves as the upright ofthe wheel assembly and as such supports the wheel-hub member 174.Serving as the upright, the gear casing 350 can also include aconnection arrangement 358 for one or more suspension arms 245 and/or aconnection arrangement 359 for a steering rod 260 (e.g., a pushrod).Connection arrangements 358, 359 can include joints or bearings asneeded for specific implementations of the embodiments of the invention.In embodiments, the wheel assembly 150 includes a sub-frame 161configured to be mounted to a reference frame, e.g., a chassis of avehicle. In embodiments, the wheel assembly 150 also includes any or allof: one or more suspension arms 245 linking the gear casing 350 to thesub-frame 161; a steering rod 260 linking a steering actuator (notshown) to the sub-frame 161; and/or a driveshaft member 180 configuredto rotate one or more components of the gearing assembly. Inembodiments, the wheel assembly 150 can include a brake assembly 177,interposed between the gear casing 350 and the wheel-hub member 174.

In embodiments, wheel assemblies, including any or all of the componentsdescribed hereinabove, can be provided in opposing pairs, or installedon a vehicle in opposing pairs. Thus, any illustration of a wheelassembly or a wheel-assembly component in the accompanying figures maybe appropriate for installation on one side or the other of a vehicle,and a skilled artisan will understand that a ‘mirror-image’implementation would be appropriate for the opposing side of thevehicle.

In embodiments, wheel assemblies as disclosed herein can be employedwith wheels which are axle-less and/or independently-suspended. In somevehicles, it can be that a first opposing pair of wheels is axle-lessand independently-suspended while a second opposing pair of wheels uses‘conventional’ or ‘prior-art’ arrangements of an axle and suspensionsystem. In other vehicles, it can be that all opposing pairs of wheelsare axle-less and independently-suspended. Some vehicles may implementthe disclosed embodiments with respect to wheel assemblies and steeringsystems only at a first pair of wheels as disclosed herein, and someother vehicles may implement the embodiments at all wheels.

As illustrated in FIGS. 1 and 2, the term ‘inward(s)’ or the equivalent‘inward-facing’ means a face or side facing towards the centerline of avehicle, while the complementary term ‘outward(s)’ or the equivalent‘outward-facing’ means facing away from the vehicle. For example, an‘inward-facing view’ in the set of attached drawings is a view of a facethat is inward-facing.

Referring now to FIG. 2, a vehicle 100 includes at least one pair ofopposing wheel assemblies 150 _(R), 150 _(L) mounted to the vehicle, forexample by mounting respective sub-frames 161 _(R), 161 _(L) to areference frame 110, e.g., the chassis, of the vehicle. The right-side(on the left side in the front view illustrated in FIG. 2) wheelassembly 150 _(R) is shown as a mirror image of the left-side wheelassembly 150 _(L) of FIG. 1.

FIGS. 3A and 3B show two views of an exemplary gear casing 350 accordingto embodiments, in which features of an upright are incorporated in thedesign of the gear casing. The gear casing 350 comprises a gear housing360 which has an internal space adapted for accommodating therein acompact gearing assembly (not shown in FIGS. 3A-B) and a lubricantcompartment 370 for a liquid lubricant, e.g., an oil, radially displacedfrom the gear housing 360. A first opening 356, on the inward-facingside of the gear casing 350 is provided for making a connectiontherethrough between a drivetrain member (e.g., a driveshaft) and thegearing assembly. A second opening 357 is provided on the outward-facingside of the gear casing 350, for making a connection therethroughbetween a wheel-hub assembly member and the gearing assembly.

According to some embodiments, suspension connecting arrangements 358are provided for bearinged connections with suspension arms. In someembodiments, suspension connecting arrangements 358 define a steeringaxis for the wheel. In some embodiments, any of the suspensionconnecting arrangements 358 can include one or more connection ports. Insome embodiments, the wheel is steerable, and a steering rod connectionarrangement 359 is provided for connecting with a steering rod. In someembodiments, one or more connection arrangements 358, 359 is/are formedat the gear housing 360 at a given radial distance from a centrallongitudinal axis (indicated in FIG. 3A by arrow 1980) of the gearhousing 360, wherein the given distance from the central axis 1980 isless than a radial distance to a periphery of the lubricant compartment370. For example, the steering rod connection 359 of FIG. 3A is at aradial distance from central axis 1980 less than a radial distance tothe point marked with an ‘X’ on the outer periphery of the lubricationcompartment 370.

A non-limiting example of a compact gearing assembly 380 comprising acompound planetary gear system is illustrated in FIGS. 4A-B. Aconstant-velocity (CV) joint 381 is provided for engagement with adrivetrain member, e.g., a driveshaft (not shown), although in otherexamples other types of joints (other than CV joints) can be suitablefor mediating between the driveshaft and the gearing assembly 380. Thedriveshaft is arranged, e.g., via the CV joint 381, to turn the sun gear385 (shown in FIG. 4B) of the planetary gear system. The sun gear 385 isengaged (i.e., meshed) with a first section of each of a plurality ofcomposite planet gears 384 mounted to and supported by a planet-gearcarrier 386. The composite planet gears 384 are arranged so that thefirst section of each planet gear 384 has a first radius and a secondsection of each planet gear 384 has a second radius. In the exampleshown in FIG. 4A, the second radius is smaller than the first radius,and the second section of each planet gear 384 is engaged with a ringgear 383. The second section is disposed inwardly of the first section(meaning that the second section is closer to the first opening 356 ofFIGS. 3A-B when installed in the gear housing 360 than is the secondsection), such that the ring gear 383 is also disposed inwardly from theportion of the sun gear 385 that engages with the planet gears. Thecompact gearing assembly 380 of FIGS. 4A-B is configured to operate asfollows: 1. Torque applied by the driveshaft (180, not shown in FIGS.4A-B) via, e.g., a CV joint 381, causes the sun gear 385 to rotate. 2.The rotation of the sun gear 385 causes the planet gears 384 to rotate.3. The rotation of the planet gears causes the plurality of planet gears384 to ‘orbit’ the sun gear 385 around the interior of the ring gear 383(which, in some embodiments, is interiorly attached to the gear housing360). 4. The orbiting of the plurality of planet gears 384 rotates theplanet-gear carrier 386. 5. The planet-gear carrier 386 is mechanicallycoupled with the wheel-hub member 174, and therefore the rotation of theplanet-gear carrier 386 turns the wheel of the vehicle. The gearingassembly 380 of FIG. 4A also includes a drive shaft support bearing 184and/or a wheel-hub bearing 173 in respective inwardly-disposed andoutwardly-disposed bearinged contact with the rotating planet gearcarrier 386. The drive shaft support bearing 184 is configured tosupport the driveshaft and/or CV joint 381 and/or mediate between aninwardly-disposed portion of the rotating planet gear carrier 386 andthe gear housing 360. The wheel-hub bearing 173 is interiorly attachedto the gear casing 360 to mediate between an outwardly-disposed portionof the rotating planet gear carrier 386 and the gear housing 360.

FIGS. 5A-B show the gear casing 350 of FIGS. 3A-B, with the compactgearing assembly 380 of FIGS. 4A-B installed in the gear housing 360.FIG. 6A shows the same assembly of the gear casing 350 with the gearingassembly 380 as was shown in FIGS. 5A-B, along with drivetrain member180 connected to CV joint 381, and a typical brake assembly 177interposed between the gear housing 360 and the wheel-hub member 174. Inan example, the maximal radius of gear casing 350 is equal to or smallerthan the maximal radius of a brake assembly 177. FIG. 6B is across-sectional view (view A-A indicated in FIG. 6A) of the sameassembly. The interior volume of the lubrication compartment 370 isradially displaced from the gear housing 360 and from the gearingassembly 380 housed within.

It can be desirable to use a liquid lubricant (oil) and not a grease forlubricating the gearing assembly 380, inter alia in order to optimizegear performance and life-cycle cost. During operation of the gearingassembly 380, liquid lubricant (e.g., an organic or non-organic oil)circulates between the lubrication compartment 370 and the drive-gearvolume 364 to lubricate the gearing assembly, where the circulationresults from gear operation and external forces acting upon the gearcasing 350, i.e., without deploying a mechanical pump for oilcirculation. The lubrication compartment 370 is in fluid communicationwith an interior ‘drive-gear volume’ 364 (illustrated in FIGS. 8A-B) ofthe gear housing 360 via—in some embodiments: exclusively via—one ormore lubrication passages 372. In some embodiments, a dimension and/orposition of one or more lubrication passages 372 is based on optimizingone or more of (and not exhaustively): lubricant quantity in thelubricant compartment 370; required lubricant flow to and/or from thedrive-gear volume 364;

sump volume and position; and design of the gearing assembly 380. Insome embodiments, there is a single continuous lubrication passage 372(not shown). In an example, a single continuous lubrication passage 372extends circumferentially from a point at the lower end of bottommostlubrication passage 372 ₁ in FIG. 6B and/or to a point at the upper endof topmost lubrication passage 372 ₂ in FIG. 6B. In another example, asingle continuous lubrication passage 372 extends circumferentially fromany point along the length of bottommost lubrication passage 372 ₁and/or to any point along the length of topmost lubrication passage 372₂. In another example, a single continuous lubrication passage 372extends circumferentially from any point below the lower end ofbottommost lubrication passage 372 ₁ and/or to any point along thelength of topmost lubrication passage 372 ₂. In embodiments, two or morediscrete lubrication passages 372 are provided. In the non-limitingexample of CFIG. 6B (and FIG. 8A), two discrete lubrication passages 372₁, 372 ₂ are provided, where a bottommost lubrication passage 372 ₂ isarranged to be entirely below a ‘half-height level’ (indicated by arrow980) corresponding to a central longitudinal axis of the gearingassembly 380 i.e., to half the height of the gearing assembly 380. Inother examples, the bottommost lubrication passage 372 ₁ extendscircumferentially from a point below the half-height level 980 to apoint above the half-height level 980. In other examples involvingmultiple lubricant passages 372, a bottommost one of the lubricantpassages, e.g., passage 372 ₁, is disposed to be at least in part belowthe half-height level 980 corresponding to the central axis of thegearing assembly 380, and a topmost one of the lubricant passages, e.g.,passage 372 ₂, is disposed to be at least in part above the central axisof the gearing assembly 380.

One or more flow-regulation devices 378, e.g., a baffle, can be providedwithin the lubrication compartment 370, typically (as shown in FIG. 6B)but not necessarily above the halfway height 980. The flow-regulationdevice 378 can have any number of oil-management functions, including,but not exhaustively: slowing the return of oil from the drive-gearvolume 364 to the lubrication compartment 370; de-foaming the returningoil; and/or filtering the returning oil.

In the example of FIGS. 3A-B, 5A-B and 6A-B, the design of the gearcasing 350 calls for a single lubrication compartment 370. In someembodiments, the single lubrication compartment 370 is located forwardof the gear housing 360. A forward-located lubrication compartment 370may facilitate functional requirements, for example for connecting to asteering assembly, and/or for allowing enough space for a brakeactuator. A forward-located lubrication compartment 370 may takeadvantage of the usual direction or rotation of the gearing assembly 380(e.g., of the planet gear carrier 383) in facilitating the oilcirculation regime in the absence of a dedicated mechanical pump. FIG. 7shows an example of a gear casing 350 comprising two lubricationcompartments 370 ₁, 370 ₂—one forward of the gear housing 360 and oneaft. In some embodiments, the two lubrication compartments 370 ₁, 370 ₂are fluidly connected with each other, directly and/or through the gearhousing 360. Any or all of the features disclosed herein for a‘single-compartment’ lubrication system, such as (and not exhaustively)lubrication passages and flow-regulation devices, are equally applicablein the ‘dual-compartment’ lubrication system of FIG. 7.

In embodiments, a gear casing 350 can be fabricated using any suitabletechnique or combination of techniques, such as casting, additivemanufacturing, and/or subtractive manufacturing (e.g., machining,electro-erosion, etc.). According to some embodiments, a gear casing 350comprises multiple portions, fabricated separately as component parts,and subsequently joined to form the gear casing 350. We now refer toFIGS. 8A-B, which schematically illustrate a non-limiting example of agear casing 350 comprising two portions—first gear casing portion 351which is substantially inward-facing, and second casing portion 352which is substantially outward-facing. In other examples, a gear casing350 comprises more than two portions. The two portions 351, 352 in theexample of FIGS. 8A-B are designed such that neither one comprises acomplete gear housing 360 or complete lubrication compartment 370.Instead, the first portion 351 comprises a first section 360 _(A) of thegear housing 360 and first section 370 _(A) of the lubricationcompartment 370, while the second portion 352 comprises a second section360 _(B) of the gear housing 360 and a second section 370 _(B) of thelubrication compartment 370. The joining of the two portions 351, 352 isthus effective to form both the gear housing 360 and the lubricationcompartment 370. The drive-gear volume 364, which is configured toaccommodate a gearing assembly 380, is similarly ‘split’ between the twoportions 351, 352 such that the joining of the two portions 351, 352forms the drive-gear volume 364. In other examples, a gear casing 350comprises two portions that are dissimilar from the two portions 351,352 of FIGS. 8A-B in any number of design aspects but which when joinedtogether form the same gear casing 350. For example, the two portions351, 352 can be designed so that a first one of the gear housing 360 andthe lubrication compartment 370 is formed entirely in one of the twoportions 351, 352, while the second one of the gear housing 360 and thelubrication compartment 370 is not, i.e., is split between the twoportions 351, 352. Even among the design alternatives which split thegear housing 360 and the lubrication compartment 370 between the twoportions 351, 352, an internal volume of the lubrication compartment 370and/or of the gear housing 360 (i.e., the drive-gear volume 364) might,in an illustrative example, be formed entirely in one portion while thesecond portion has a flat ‘cover’ for the formed volume in the oppositeportion. In embodiments, and as illustrated in FIG. 8A, the one or morelubrication passages 372 are formed entirely in one of the two portions351, 352; in the illustrated example, they are formed exclusively in thefirst portion 351.

Joining the component portions of the gear housing 350, e.g., first andsecond portions 351, 352, can be accomplished using any of the knowntechniques such as fastening, welding, brazing, adhesive-bonding, orsimply closing, e.g., with retaining elements such as nuts and bolts, orscrews, on a sealant or on a gasket. FIG. 9 illustrates an exemplarygasket 354 suitable for use in joining the portions 351, 352 of FIGS.8A-B. In some embodiments, the one or more lubricant passages 372 can beformed in the gasket 354 itself, additionally to or alternatively tolubricant passages 372 formed in one of the portions 351, 352.

Referring now to FIGS. 10A-C, an assembly of a gear casing 350 and agearing assembly 380 is illustrated together with a wheel-hub member 174and a brake assembly 177. A brake caliper 178 and associated caliperpistons 179 also shown, mounted to the brake assembly 177.

It can be desirable to design the lubrication compartment 370 so thatits radial extension from the gear housing 360 (the dimension indicatedin FIG. 10B by arrow H₃₇₀) along the circumference of the adjacent gearhousing 360 substantially exceeds its thickness (the dimension indicatedin FIG. 10B by the arrow W₃₇₀). Inter alia, this provides for anadequately long section of the circumference of the gear housing 360 tobe in fluid communication with the drive-gear volume 364 withoutrequiring too large a quantity of lubricant in the lubricant compartment370. Thus, it can be desirable to achieve a minimal thickness W₃₇₀ tothe extent practical. As shown in the partial front view of FIG. 10B,thickness W₃₇₀ can be less than half the thickness of the gear housing360 (the dimension indicated in FIG. 10B by the arrow marked W₃₆₀). Insome embodiments, the thickness W₃₇₀ is less than 45%, or less than 40%,or less than 35%, or less than one-third, or less than 30%, or less thanone-quarter, of the thickness W₃₆₀.

While the gear housing 360 can thus have a thickness (W₃₆₀) that is 2times, or 3 times, or more than 3 times the thickness of the lubricationcompartment 370 (W₃₇₀), minimizing the thickness of the gear housing 360itself can be useful for facilitating the integration of the gear casing350 into a wheel assembly 150 where space can be scarce and where it canbe desirable to minimize the ‘unsprung’ weight of these components. Thethickness W₃₆₀ of the gear housing 360 is shown in the rear elevationview of FIG. 10C, where the thickness W₃₆₀ can be compared to the widthof the brake caliper 178 (including caliper pistons 179), said widthbeing the dimension indicated in FIG. 10C by the arrow W₁₇₈. Both ofthese dimensions are in a direction parallel to the central axis of thegearing assembly 380, which is indicated in FIG. 10C by the arrow marked1980. (All widths and dimensions indicated in FIGS. 10B and 10C areparallel to the central axis 1980.) The thickness W₃₆₀ is less than 130%of the width W₁₇₈, or less than 110% of the width W₁₇₈, or less than100% of the width W₁₇₈. The compactness of the gearing assembly 380 canbe a key factor in designing a gear housing 360 with a minimalthickness. The thickness of the gearing assembly 380, the dimensionindicated in FIG. 10C by the arrow W₃₈₀, is less than 120% of thethickness of the width W₁₇₈, or less than 110% of the width W₁₇₈, orless than 100% of the width W₁₇₈, or less than 90% of the width W₁₇₈.

Referring now to FIG. 11, a gearing assembly 380 according toembodiments is illustrated within a wheel 172 having a tire mounted onthe wheel rim (not shown in FIG. 11 because it is obscured by the tire),the wheel 172 being mounted to wheel-hub member 174. It can be seen thatthe compact gearing assembly 380 is positioned, inter alia forspace-saving purposes, in its entirety between the wheel-hub member 174and a plane defined by an inward-facing rim (not shown) of a wheelmounted to the wheel-hub member 174, the plane of the rim beingindicated in FIG. 11 by the arrow marked 985.

FIG. 12 is a schematic drawing of a first portion 351 of a gear casing350 together with a gearing assembly 380 placed within the correspondingfirst-portion section 364 _(A) of drive-gear volume 364. In embodiments,a minimum level of lubricant oil is maintained in the lubricantcompartment 370 (the corresponding first-portion part 370 _(A) is shownin FIG. 12). In some embodiments, optimal performance of the gear isachieved when a suitable level of lubricant level is maintained, i.e.,when the gearing assembly is not operating. This suitable level,indicated in FIG. 12 by arrow 981, is between 20% and 50% of the heightof the gearing assembly 380, i.e., the distance between the bottom ofthe gear (indicated in FIG. 12 by arrow 982) and the suitable level 981.In some embodiments, the suitable level is between 25% and 45% of thegear height, and in other embodiments between 30% and 40% of the gearheight, or about one-third of the gear height. As described hereinabove,an array of one or more lubricant passages 172 is disposedcircumferentially around a portion of the gear housing 360, thelubricant-passage array arranged for flow therethrough of a lubricantoil (for lubrication of the gearing assembly 380) between the lubricantcompartment 370 and the gear housing 360. In embodiments in which thearray comprises two or more lubricant passages 372, a suitablemaintained level of lubricant level is at the height of the top of thebottommost lubricant passage, e.g., passage 372 ₁ of FIG. 8A, or within±1 cm thereof or within ±2 cm thereof. In some embodiments in which thearray comprises two or more lubricant passages 372, a majority oflubricant flow through the topmost lubricant passage, e.g., passage 372₂ of FIG. 8A, during gear operation is oil ‘returning’ from gear housing360 to the lubricant compartment 370, a direction indicated by arrow1055 in FIG. 12. The ‘returning’ to the lubricant department 370 caninclude, for example, flowing, splashing, and/or foaming. In embodimentsin which the array comprises two or more lubricant passages 372, asuitable location for flow-regulating device 378 is below the topmostlubricant passage, e.g., passage 372 ₂ of FIG. 8A. In an exampleillustrated in FIG. 13, the interior volume 371 of the lubricantcompartment 370 comprises a lower section 371 ₁ above theflow-regulating device 378 and an upper section 371 ₂ above theregulating device 378. During normal gear operation, the upper section371 ₂ holds more residues from returning oil, air, and oil-air foam thanthe lower section 371 ₁, while the lower section 371 ₁ holds more liquidoil than the upper section 371 ₂.

The present invention has been described using detailed descriptions ofembodiments thereof that are provided by way of example and are notintended to limit the scope of the invention. The described embodimentscomprise different features, not all of which are required in allembodiments of the invention. Some embodiments of the present inventionutilize only some of the features or possible combinations of thefeatures. It will be appreciated by persons skilled in the art that thepresent invention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present inventionincludes both combinations and sub-combinations of the various featuresdescribed hereinabove, as well as variations and modifications thereofthat are not in the prior art, which would occur to persons skilled inthe art upon reading the foregoing description.

In the description and claims of the present disclosure, each of theverbs, “comprise”, “include” and “have”, and conjugates thereof, areused to indicate that the object or objects of the verb are notnecessarily a complete listing of members, components, elements or partsof the subject or subjects of the verb. As used herein, the singularform “a”, “an” and “the” include plural references unless the contextclearly dictates otherwise.

The invention claimed is:
 1. A gear casing for a wheel-hub assembly, thegear casing comprising: a. a gear housing comprising a drive-gear volumefor accommodating therewithin a gearing assembly that is positioned tomediate between a drivetrain member and a wheel-hub member, thedrive-gear volume being in fluid communication with opposing first andsecond openings formed in the gear housing for respectivegearing-assembly connections therethrough with the drivetrain member andthe wheel hub member; b. a lubricant compartment radially displaced fromthe drive-gear volume and in fluid communication therewith exclusivelyvia an array of one or more lubricant passages disposedcircumferentially around a portion of the gear housing, thelubricant-passage array arranged for flow therethrough of agearing-assembly lubricant between the lubricant compartment and thegear housing; and c. a plurality of casing portions, wherein at leastone of the gear housing and the lubricant compartment is formed by ajoining of at least two of the plurality of casing portions, each of thejoined casing portions comprising at least a part of a respectiveinterior surface of at least one of the gear housing and the lubricantcompartment.
 2. The gear casing of claim 1, wherein both the gearhousing and the lubricant compartment are formed by the joining.
 3. Thegear casing of claim 1, wherein the lubricant-passage array is formedexclusively in one joined casing portion.
 4. The gear casing of claim 1,wherein the plurality of casing portions includes a gasket interposedbetween two other casing portions of the plurality of casing portions,and the lubricant-passage array is formed in the gasket.
 5. The gearcasing of claim 1, wherein the lubricant-passage array comprises aplurality of discrete lubricant passages.
 6. A gear casing for awheel-hub assembly, the gear casing comprising: a. a gear housingcomprising a drive-gear volume for accommodating therewithin a gearingassembly that is positioned to mediate between a drivetrain member and awheel-hub member, the drive-gear volume being in fluid communicationwith opposing first and second openings formed in the gear housing forrespective gearing-assembly connections therethrough with the drivetrainmember and the wheel hub member; and b. a lubricant compartment radiallydisplaced from the drive-gear volume and in fluid communicationtherewith exclusively via an array of one or more lubricant passagesdisposed circumferentially around a portion of the gear housing, thelubricant-passage array arranged for flow therethrough of agearing-assembly lubricant between the lubricant compartment and thegear housing, wherein a bottommost one of the lubricant passages isdisposed to be at least in part below a central axis of the gearingassembly, and a topmost one of the lubricant passages is disposed to beat least in part above the central axis of the gearing assembly.
 7. Thegear casing of claim 6, wherein at least a part of the bottommostlubricant passage is lower than a lowest part of the drive-gear volume.8. The gear casing of claim 1, configured such that all lubricant flowsbetween the lubricant compartment and the gear housing are due to atleast one of: (i) forces generated by operation of the gearing assembly;and (ii) external forces acting upon the wheel-hub assembly.
 9. A gearcasing for a wheel-hub assembly, the gear casing comprising: a. a gearhousing comprising a drive-gear volume for accommodating therewithin agearing assembly that is positioned to mediate between a drivetrainmember and a wheel-hub member, the drive-gear volume being in fluidcommunication with opposing first and second openings formed in the gearhousing for respective gearing-assembly connections therethrough withthe drivetrain member and the wheel hub member; b. a lubricantcompartment radially displaced from the drive-gear volume and in fluidcommunication therewith exclusively via an array of one or morelubricant passages disposed circumferentially around a portion of thegear housing, the lubricant-passage array arranged for flow therethroughof a gearing-assembly lubricant between the lubricant compartment andthe gear housing; and c. a plurality of lubricant compartments radiallydisplaced from the drive-gear volume, each lubricant compartment beingin fluid communication therewith exclusively via a respective array ofone or more lubricant passages disposed circumferentially around aportion of the gear housing, the respective lubricant-passage beingarrays arranged for flow therethrough of a gearing-assembly lubricantbetween the lubricant compartment and the gear housing.
 10. A wheelassembly comprising: a. a gear casing comprising: i. a gear housingcomprising a drive-gear volume for accommodating therewithin a gearingassembly that is positioned to mediate between a drivetrain member and awheel-hub member, the drive-gear volume being in fluid communicationwith opposing first and second openings formed in the gear housing forrespective gearing-assembly connections therethrough with the drivetrainmember and the wheel hub member; ii. a lubricant compartment radiallydisplaced from the drive-gear volume and in fluid communicationtherewith exclusively via an array of one or more lubricant passagesdisposed circumferentially around a portion of the gear housing, thelubricant-passage array arranged for flow therethrough of agearing-assembly lubricant between the lubricant compartment and thegear housing; b. the gearing assembly positioned to mediate between thedrivetrain member and the wheel-hub member, the gearing assemblydisposed within in the gear casing and comprising a compound planetarygear train comprising (i) a sun gear in bearinged connection with thedrivetrain member of the vehicle so as to be rotated thereby, (ii) acarrier in bearinged connection with the wheel-hub member, and (iii) aplurality of composite planet gears each having multiple radii; c. asub-frame configured to be mounted to a reference frame of a vehicle; d.a suspension arm linking the sub-frame to a first connection portion ofthe gear casing; and e. a steering system member connected distally to asecond connection portion of the gear casing and configured to rotatethe wheel-hub member about a steering axis.
 11. The wheel assembly ofclaim 10, wherein the bearinged connection with the wheel-hub member isvia a wheel-hub bearing assembly interiorly attached to the gear casing.12. The wheel assembly of claim 10, wherein the planet gears are meshedwith a ring gear interiorly attached to the gear casing.
 13. A wheelassembly comprising: a. a drivetrain member and a wheel-hub member, anda gearing assembly coupled to the wheel-hub member and positioned tomediate between the drivetrain member and the wheel-hub member; b. agear casing comprising: i. a gear housing comprising a drive-gear volumefor accommodating therewithin the gearing assembly, the drive-gearvolume being in fluid communication with opposing first and secondopenings formed in the gear housing for respective gearing-assemblyconnections therethrough with the drivetrain member and the wheel hubmember; ii. a lubricant compartment radially displaced from thedrive-gear volume and in fluid communication therewith exclusively viaan array of one or more lubricant passages disposed circumferentiallyaround a portion of the gear housing, the lubricant-passage arrayarranged for flow therethrough of a gearing-assembly lubricant betweenthe lubricant compartment and the gear housing; c. the gearing assemblypositioned to mediate between the drivetrain member and the wheel-hubmember, the gearing assembly disposed within in the gear casing andcomprising a compound planetary gear train comprising (i) a sun gear inbearinged connection with the drivetrain member of the vehicle so as tobe rotated thereby, (ii) a carrier in bearinged connection with thewheel-hub member, and (iii) a plurality of composite planet gears eachhaving multiple radii; d. a brake assembly coupled to the wheel-hubmember, the brake assembly being characterized by having a brake caliperconnected thereto, wherein a thickness of the gear housing through thedrive-gear volume is less than 120% of a width of the brake caliper, thethickness and the width both being in a direction parallel to a centralaxis of the gearing assembly.
 14. The wheel assembly of claim 13,wherein a thickness of the gearing assembly is less than 110% of a widthof the brake caliper, the thickness and the width both being in adirection parallel to a central axis of the gearing assembly.
 15. Thewheel assembly of claim 13, wherein the gearing assembly is disposedentirely between the wheel-hub member and a plane defined by aninward-facing rim of a wheel mounted to the wheel-hub member.
 16. Avehicle comprising: a pair of opposing wheel assemblies, the wheelassemblies being according to claim 10; a corresponding pair of wheels;and the reference frame.
 17. The gear casing of claim 1, wherein athickness of the lubricant compartment is less than half of a thicknessof the gear housing, the thickness of the lubricant compartment and thethickness of the gear housing both being in a direction parallel to acentral axis of the gearing assembly.
 18. The gear casing of claim 6,wherein a thickness of the lubricant compartment is less than half of athickness of the gear housing, the thickness of the lubricantcompartment and the thickness of the gear housing both being in adirection parallel to a central axis of the gearing assembly.
 19. Thegear casing of claim 9, wherein a thickness of the lubricant compartmentis less than half of a thickness of the gear housing, the thickness ofthe lubricant compartment and the thickness of the gear housing bothbeing in a direction parallel to a central axis of the gearing assembly.20. The wheel assembly of claim 10, wherein a thickness of the lubricantcompartment is less than half of a thickness of the gear housing, thethickness of the lubricant compartment and the thickness of the gearhousing both being in a direction parallel to a central axis of thegearing assembly.
 21. The wheel assembly of claim 13, wherein athickness of the lubricant compartment is less than half of a thicknessof the gear housing, the thickness of the lubricant compartment and thethickness of the gear housing both being in a direction parallel to acentral axis of the gearing assembly.
 22. The wheel assembly of claim13, wherein the bearinged connection with the wheel-hub member is via awheel-hub bearing assembly interiorly attached to the gear casing. 23.The wheel assembly of claim 13, wherein the planet gears are meshed witha ring gear interiorly attached to the gear casing.